Cloud fraction represents the portion of sky in each pixel that is covered by clouds. Satellites can measure cloud fraction over the entire atmosphere and for all types of clouds. Since most clouds reflect incoming sunlight very well and trap heat escaping from the Earth's surface, cloud fraction is an important parameter in studies of our planet's radiant energy budget. (Data from International Satellite Cloud Climatology Project [ISCCP]). Sensor: No Satellite/ISCCP. Data Start Date: 7/1/83. Data End Date: 6/30/91.